Dolphins rely heavily on sound production to navigate, communicate, locate prey and in social behaviour, including group cohesion and recognition of familiar individuals. The frequency of the sounds produced by a bottlenose dolphin ranges from 0.2 to 150 kHz which overlaps on the sound produced by recreational boats (100 Hz and 10 kHz) (Hildebran 2009; Picciulin et al, 2010; Rako et al, 2013). Research has suggested that in noisy environments, dominated by recreational boating noise, dolphins may adjust call rates and shift their whistle frequencies to the range with lower noise interference in order to increase transmission efficiency and detectability of their acoustic signals (Rako-Gospic and Picciulin, 2016; Luis et al. 2014). Disturbances can hinder the core biological activities of dolphins and thus the health and condition, in addition, can cause displacement from areas of high impact to areas of low impact. This disturbance and displacement can greatly affect the natural state of the dolphins (feeding, resting, social, calving rate etc).
We currently have little information on the frequency range or call rates on the Burrunan dolphin, thus making it difficult to assess if there is alterations in that frequency in response to boat disturbances or a shift in their natural state.
We assess the acoustic characteristics of dolphins in relation to behaviour, vessel interactions and noise impact.
Rebecca Wellard; Kate Charlton-Robb; Christine Erbe; Bob Wong (2016) Whistle characteristics of newly defined species, the Burrunan dolphin (Tursiops australis), in coastal Victorian waters in Australia. The Journal of the Acoustical Society of America 140, 3416 (2016); doi: http://dx.doi.org/10.1121/1.4970980
A newly defined species, the Burrunan dolphin (Tursiops australis), was described in 2011 by Charlton-Robb et al., and is endemic to southern and south-eastern Australian coastal waters. This species’ distribution is characterized by small, isolated, and genetically distinct populations. With only two known populations in Victoria, the species is now listed as “Threatened” under the Victorian Flora and Fauna Guarantee Act. Describing and quantifying the vocal repertoire of a species is critical for subsequent analysis of signal functionality, geographic variation, social relevance, and identifying threats associated with anthropogenic noise. Here, we present the first quantitative analysis of whistle characteristics for the species, undertaken on these endemic Victorian populations. Vocalizations of T. australis were recorded during population based surveys in 2007 and 2014 across the Gippsland Lakes and Port Phillip Bay, Victoria. Acoustic parameters of whistles were measured including minimum frequency (fmin), maximum frequency (fmax), start frequency (sf), end frequency (ef), delta frequency (df= fmax-fmin), duration, number of extrema, number of inflection points, and number of steps. We review and compare T. australis whistle features to the two other bottlenose dolphins, T. truncatus and T. aduncus, to assess the similarity and/or differences between the sounds of the three species of bottlenose dolphins.